1. Chemical &
Biological
Engineering.
Anaerobic Digesters: The Effect Of Hydrogen Added In The Form Of Micro-bubbles
Student:
Kuganathan Padmanathan
kpadmanathan1@sheffield.ac.uk
Supervisor: 2014
Professor Will Zimmerman
Dr. James Hanotu
Depleting fossil fuels, Oil and Gas need a suitable
replacement. Biogas produced from an anaerobic
digestion (AD) system is an excellent solution for solid
waste management and production of sustainable
energy.
1. Al-Mashhadani, M. K., (2013). Application of Micro bubbles Generated by Fluidic Oscillation in the Anaerobic Digestion
Process.
2. Michael H. Gerardi (2003). The Microbiology of Anaerobic Digesters. New Jersey: John Wiley & Sons. 192
3. Tchobanoglous, G., Burton, F. and Stensel, H., 2003. Wastewater engineering. 1st ed. Boston: McGraw-Hill.
Potential increase
in CH4 using H2
From the observation
of the preliminary
results of the study,
the production of CH4
is indeed possible
with the introduction
of H2 into the AD
CH4 production is
affected by
various
parameters
The biological
reaction of the
methane producing
bacteria are effected
by pH, temperature,
and other parameters.
Acidogenesis
Process (Studies)
Since the production
of CH4 is primarily
from the acetic acid
reaction (70%), further
study on the volatile
fatty acids production
is needed.
H2 Availability
(Large Scale)
As H2 is itself a
valuable energy
source, the availability
of H2 source should
be considered for
large scale
implementation
Preparation of raw material:
Kitchen Waste
Assessment of raw material
suitability : pH, BOD, COD, VFA
Addition of (H2 + N2) and (H2 +
CO2) into the kitchen waste in the
form of micro-bubbles
Analysis of the outlet gas stream
from the AD using gas analyzer
0
10
20
30
40
50
0 2 4 6 8 10 12 14 16
GASPRODUCTION(%)
TIME (DAYS)
Gas Production in Anaerobic Digester
Carbon Dioxide (CO2) production
Methane (CH4) production
0
2
4
6
8
0 2 4 6 8 10 12 14 16
pHLEVEL
TIME (DAYS)
pH LEVEL
Characteristics Value
Biological Oxygen Demand, BOD (g/l) 1.79
Chemical Oxygen Demand, COD (g/l) 32.6
Volatile Fatty Acids, VFA (mg/l) 4636
Sulphate, (mg/l) 774
The production of CO2 is more evident
during the first 15 days of the digestion
process compared to CH4
After the 9th day, CO2 production
increases indicating the fermentation
process and CH4 producing bacteria are
not active at this stage
High amount of Oxygen (O2) presence in
the AD inhibits the production of CH4 in
the first few weeks [Ref 3]
The change in pH level indicates the
presence of VFAs produced during the
fermentation process
Higher amount of COD observed in the
AD implies the capacity to produce high
amount of CH4 [Ref 2]
Previous study proved that when Carbon Dioxide
(CO2) and Nitrogen (N2) were added to the digestion
system in the form of micro-bubbles, the system
performed better in comparison to fine bubbles.
BACKGROUND INTRODUCTION
Micro-bubble Technology
PURPOSE OF RESEARCH
EXPERIMENTAL METHOD
REFERENCES
CONCLUSION
RESULTS
AIM:
Since H2 is a
limiting reactant in
AD, additional H2
is added in the
form of micro-
bubbles to
evaluate the
production of CH4.
Figure 1: Methane Producing Pathway
Table 1: Physical characteristics of food waste
Figure 3: Kitchen Waste in the AD
Figure 2: Experiment Apparatus Set-Up of Airlift Anaerobic Digester
Gas Analyzer Temperature Controller
Flow meter
Fluidic Oscillator
pH
meter
Heater
Diffuser
Gas Outlet
Gas
Inlet
5th day 15th day
Improves
mass and heat
transfer
between liquid
and gas phase
Lower energy
demand
compared to
conventional
AD
Significant
removal of
CO2 and H2S
in airlift AD
[Ref 1].

2. Biogas
50-70 % CH4
30-50 % CO2
Digested
SubstrateAnaerobic
Digester
Uses:
 Electricity
 Heat
 Transportation
fuel
 Natural Gas
Organic
Substrate
Why Use H2 ?
Increases CH4
production and
reduces CO2
content in AD
30% of total CH4
production in AD is
from H2 utilization
(Hydrogenotrophic
Methanogens)

3. CH4 + CO2
H2, CO2Acetic Acid
Volatile
Fatty Acids
Soluble
Organic
Matter
Complex
Organic
Substrate
1
2
3
3
30 %70 %
1. Hydrolysis
2. Fermentation
3. Acetogenesis
4. Methanogenesis